In 2002 there were more than 132,000 infants born from multiple pregnancies in the US, the highest number ever recorded. Since 1980 this rate has risen dramatically, due primarily to infertility treatments in combination with the trend of childbearing at older ages. The use of assisted reproductive technologies carries a 30-50% risk of resulting in a multiple pregnancy, depending on the medications and techniques used. Older maternal age requires more aggressive therapies to achieve a pregnancy, including transferring more embryos. The two most important factors affecting perinatal mortality are gestational age and relative birth weight; with each additional fetus, both of these factors are compromised. Compared to singletons, infants of multiple pregnancies are much more likely to be born early preterm and very low birth weight, important factors contributing to their excess morbidity and mortality. We do not have contemporary, nationally representative, population-based estimates of the increased infant mortality risk associated with multiple pregnancies. The purpose of this proposed study is to determine the infant mortality risks for infants of multiple pregnancies, controlling for important maternal and fetal factors, including age, race and ethnicity, parity, smoking status, infant gender, birth weight, and gestational age, as well as factors unique to multiple pregnancies (e.g., weight discordance, gender mix, fetal death of a sibling). The central hypothesis of this proposal is that mortality risk is higher for infants of multiple pregnancies compared to singletons, and that some of this risk has been postponed from the neonatal to the post-neonatal period. The data for this study are the 1995-2000 Linked Birth/Infant Death Data Sets and the Matched Multiple Birth Data Sets. The resulting plurality-specific perinatal, neonatal, post-neonatal, and overall infant mortality risks will help practitioners counsel patients undergoing infertility treatments and considering multi-fetal pregnancy education, and more effectively manage the pre- and postnatal health of infants of multiple pregnancy.